As described in U.S. Pat. No. 6,767,281 to McKee (McKee '281), most buildings and enclosures where human activity takes place require some type of venting. The type of venting device used depends on the kind of enclosure to be vented. For example, bathrooms with showers typically have active vents with fans to vent steam to the outdoors. Kitchens, particularly in restaurants and hotels, similarly have powered vents for removing smoke, steam and other matter.
Other types of enclosures, such as attics, do not require active venting. However, such enclosures do typically require a passive vent to allow for air flow from the enclosure to outside atmosphere. This type of venting prevents a buildup of moisture in the enclosure and reduces the heat trapped in the attic space. The venting of attic spaces by this method is required by the building codes of many jurisdictions.
As used herein, the term “passive” as applied to a vent means that the vent does not include a mechanism for forcing air out of the enclosure. Rather, the vent simply includes an air conduit which allows air flow. Passive vents, including those disclosed by McKee '281, are well-known and have been extensively used in the past. Although often formed of metal, good results have been achieved more recently with plastic vents.
House attics and other similar enclosures are sometimes vented simply by one or more passive venting devices on the roof. The passive venting devices are each positioned above a ventilation passage in the roof which permits air to flow from the enclosure to the outside.
In other cases, a more sophisticated venting system is used. Such a system includes intakes, for bringing air into the enclosure, operating together with vents permitting air to flow out of the enclosure. Ideally, such a system causes outside air to flow through the enclosure. In this way, gases and vapors, including water vapor, in the enclosure are carried out of the enclosure by the air flowing through the vents. Moisture and temperature are thus equalized between the enclosure and the outside atmosphere.
On sloped roofs it is common to have intakes installed beneath the eaves for bringing air into the attic. Vents for venting air out of the attic are installed higher up on the roof, near the peak. Thus warm moist air within the enclosure rises and flows out through the higher vents. Air from the outside is taken into the enclosure through the intakes because of the pressure differential created by the outflow of air through the vents.
Part of the function of a vent is to allow the flow of air through an enclosure without permitting moisture, such as rain or snow, to enter the enclosure. Thus prior art vents have included features to prevent such entry of moisture.
U.S. Pat. No. 6,155,008 to McKee (McKee '088) discloses a passive venting device for venting a building enclosure. The device includes a base member having a vent structure therein. The vent structure is to be positioned over the ventilation passage which extends through the roof of the enclosure. The device also includes a cap member which is positioned over the vent structure to prevent rain and snow from falling directly into the vent structure and through the passage. The cap member, however, is spaced apart from the base to allow air to flow between the cap and the base and through the vent structure.
It has been found that despite the presence of a cap over the vent structure in devices such as the McKee '088 device, precipitation, such as snow, can occasionally pass into the enclosure through the vent structure. This is because the McKee device permits snow to accumulate at the base of the device near the bottom edge of the cap. Experience has shown that wind traveling along the sloped roof will often drive snow up under the cap and through the vent structure into the attic.
This problem can be exacerbated in cases where the intakes beneath the eaves become blocked, are improperly installed, do not exist, or have inadequate openings for free flow of air into the ventilated space. In such cases the vent on top of the roof, rather than the eave intake vents, can act as an intake vent. For example, where there is no air inflow from the eaves, when air flows out of one vent it must flow in through another vent. Or, air may flow out through one region of the vent structure of a vent while flowing in through another region of the vent structure. Either way, if any air flows into the vent snow or rain near the vent can be drawn into the enclosure. Any snow blown toward the vent structure will be more likely to enter if the air flow passes into the vent.
Though devices such as the McKee device are generally effective in blocking entry of rain into the attic, it has also been found that they can leak during extreme weather conditions such as torrential rain. There are at least two reasons for this. First, torrential rains are often accompanied by high winds which can drive rain into the vent structure in the same way described above with respect to snow. Second, because there is a great deal of rain falling very hard, rain can strike the device, bounce up under the cap, and enter the vent structure. As with snow, more rain will enter the attic in cases where the device is acting as a full or partial intake.
Another issue with respect to roof vents is their use in conjunction with roofing materials such as shingles, shakes or tiles. The venting device disclosed in McKee includes a wide nailing flange which is nailed to the roof to permit shingles to be lapped over the flange. Thus, on a sloped shingled roof shingles are installed on top of the flange at the top end and side ends of the flange. At the bottom, the flange overlaps the shingles. In this manner water is shed off the roof.
To provide an appropriate seal for the roof, shingles are typically lapped over the flange right up to the vent structure in the center of the device. One reason this is done is to reduce the probability that water will enter under the sides of the shingles.
Unfortunately, McKee '008 and '281 include a ventilation pathway which is open vertically to the sky. This means that precipitation falling onto the top of the vent structure may be directed straight down into the ventilation pathway and into the vent structure. Also, the vent structure of McKee includes areas below the vent structure which tend to trap moisture, thus creating a pool which may encourage mildew or other unwanted growth.
There remains a need for an attic vent structure which more effectively restricts the inflow of moisture into the space which is to be vented. The present invention solves this and other problems.